Switching devices are designed in particular to interrupt current paths in the event of a short circuit or in the event of an overcurrent. Furthermore, the switching devices may be designed with one or more poles, in particular with three poles. They can have one or more switching contact pairs for each pole. In particular, the switching devices are designed to disconnect currents of more than 100 A, in particular of several thousand A.
A release for a circuit breaker with a dielectric housing which comprises two contacts, which are pressed against one another in a sprung manner when the circuit breaker is in the connected position, per pole is disclosed in the German translation DE 691 10 540 T2 or European patent specification EP 0 455 564 B1, the entire contents of each of which is hereby incorporated herein by reference. The contacts can be separated by the effect of electrodynamic repulsion forces when the current flowing through the contacts exceeds a specific threshold value, in order in this way to limit the current. The release comprises an overload and/or short-circuit detection element in order to act on a switching mechanism which automatically disconnects the circuit breaker in the event of a fault.
Furthermore, the release comprises an operating member which responds to an overpressure which is produced in the separation zone of the contacts by an arc that is struck on electrodynamic repulsion of the contacts, in order to operate the disconnection mechanism of the circuit breaker. The operating member is a gas-tight unit which is connected exclusively to the separation zone of the contacts and comprises a moving element such as a piston or a membrane with a limited control travel. The moving element first has the overpressure applied to it, and secondly a return apparatus with a matched active force. Its movement results in tripping of the disconnection mechanism of the circuit breaker, with the return apparatus being designed with a matched active force so as to prevent inadvertent tripping in the event of a simple overload or response of a downstream current-limiting circuit breaker.
U.S. Pat. No. 3,631,369 A discloses a release with a moving armature. The armature is in the form of a bimetallic strip, and the electromagnetic release can act on it. An extension from the armature projects into the gas outlet channel of the arc quenching chamber. During disconnection, the armature is moved by the gas flow to the tripping position.
The power switching devices under consideration are, for example, so-called MCCB switching devices (Molded-Case Circuit Breakers). In the case of a switching device such as this, the current to be interrupted is interrupted before it reaches its maximum value, in that the switching contacts of the MCCB are drawn apart from one another by electromagnetic repulsion of adjacent conductors, thus interrupting the current.
Alternatively or additionally, the switching contacts may be operated, for example, by way of an actuator, which can preferably be operated electromagnetically. The actuator may be operated, for example, by an overload and/or short-circuit detection element.
A splitter stack for cooling the hot arc plasma during opening of the switching contacts is typically provided in the area of the switching contacts. Cooling the plasma down decreases the electrical conductivity such that the voltage required to maintain the arc is no longer sufficient. The arc breaks down and the current is interrupted.
In the case of the switching device mentioned initially according to EP 0 455 564 B1, the switching mechanism can be tripped not only by the overload and/or short-circuit detection element but also by a pressure-dependent operating member which acts independently thereof. The overpressure created when the arc is struck is used as a tripping criterion, and this is directly related to the arc energy. In other words, the pressure increases to a greater extent, the higher the arc energy is. Energy-selective disconnection of the switching device is therefore possible by evaluation of the overpressure.